A vinyl chloride resin is low-cost, suitable for general purpose and applied for various uses such as hard plates, hard mold products, water and sewerage pipes, valves and joints. Further, various modification methods of a vinyl chloride resin are also known.
For example, a soft polyvinyl chloride composition prepared by blending polyvinyl chloride with a liquid plasticizer such as a phthalic acid ester derivative is used in various fields, because it has flexibility and excellent strength properties. However, such a soft polyvinyl chloride composition, which contains a liquid plasticizer, has a problem of the reduced flexibility and the embrittlement due to the migration or the volatilization of the liquid plasticizer during long-term use, or during use under high temperature conditions.
Under such circumstances, in order to solve such a problem, it is proposed that polymeric plasticizers having no possibility of migration or volatilization, such as a chlorinated polyethylene, an ethylene-vinyl acetate copolymer, an ethylene-carbon monoxide-vinyl acetate copolymer, a thermoplastic polyurethane and a nitrile rubber, are blended with a polyvinyl chloride [see Japanese Patent Application Laid-open Nos. Sho 59-33345 and Sho 63-68654, etc.].
Whereas, as a compound having excellent properties such as impact resistance, and excellent processability, there is proposed a composition prepared by blending a vinyl chloride resin with an aromatic vinyl block copolymer such as a styrene-butadiene block copolymer, a styrene-isoprene block copolymer or a hydrogenated product thereof [see Japanese Patent Application Laid-open No. Hei 5-117474]. Further, the International Patent Application Publication No. WO94/06859 discloses a composition prepared by blending a specific ethylene-α-olefin copolymer with a thermoplastic resin such as a polyolefin, a polyurethane or a polyvinyl chloride, for the purpose of improving the impact resistance of those thermoplastic resin at low temperature. The aromatic vinyl block copolymer or a hydrogenated product thereof, or the specific ethylene-α-olefin copolymer can also be considered as a kind of polymeric plasticizer.
Thus, it is known that various polymers are blended with a vinyl chloride resin as plasticizers. However, it is important that the polymer to be blended is selected also in consideration of the processability as described in the Japanese Patent Application Laid-open No. Hei 5-117474.